<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8">
    <title>Document</title>
  </head>
  <body>
    <script>
      var obj = { name: 'Tom', age: 16 };
      console.log('age' in obj);		// 输出结果：true
      console.log('gender' in obj);	// 输出结果：false
    </script>
  </body>
</html>